Wayne Parham Messages: 18789 Registered: January 2001
Illuminati (33rd Degree)
Truly excellent.
I hear you about subs that are smaller than the midwoofer in the mains. It just seems "wrong." And you can get higher efficiency from a larger sub, so there's definitely an advantage in using a larger subwoofer.
But there is one place that I think having a smaller subwoofer makes sense, and that's in the flanking subs. Using a smaller cabinet there is sometimes easier to place, giving more placement options. A flanking sub can offer extension but its main purpose is blending in the upper midbass and lower midrange.
The 20" square cabinets you've described sound like they'll be perfect for this purpose. They'll likely trade a little bit of extension for midbass efficiency. That's an excellent flanking sub.
If you're also running a distant multisub or two, that's where you can really take advantage of large, powerful subs. Might be able to use the same drivers you've chosen for your flanking subs in a larger box, perhaps tuned in an EBS alignment, giving deeper extension. Or maybe choose a different driver that'll get you down into the teens. Or stay with the same cabinet - which probably offers ample extension as it is - and just run one or two more for modal smoothing.